The present invention relates to an optical semiconductor device and, more particularly, to a hermetically sealed optical semiconductor device.
At present, as an amount of information is increased, a large transmission capacity is strongly demanded. In a digital communication field, a communication speed is increasing from 0.6-Gbs modulation to 2.5-Gbs modulation.
Conventionally, as a package coped with the high-speed communication, a thin shell structure had been popular. This structure can reduce a capacitance between terminals and cope with the high-speed communication. However, the structure has the following decisive drawback. That is the welding thickness is too small to apply stem welding fixation using a laser, and the reliability of fixation cannot be improved.
As a package for solving the above drawback, a stem having a thick plate structure capable of applying laser welding fixation can be used. FIG. 3 is a longitudinal sectional view showing an optical semiconductor device having a thick plate structure. As shown in FIG. 3, the stem has the following structure. That is, lead wires 1a and 1b are hermetically insulated and fixed in a flat metal plate 3 through glass members 2. Each of the glass members 2 is in contact with the flat metal plate 3 on only a side A substantially parallel to the lead wires 1a and 1b, and only one lead wire is fixed in one of the glass members 2 surrounded by one contact side between one of the glass members 2 and the flat metal plate 3.
The glass members 2 are generally made of oxide glass, and the lead wires and the flat metal plate are generally made of iron or a nickel alloy.
In the above conventional semiconductor device, since one lead wire is fixed in a glass member surrounded by one contact side between the glass member and the flat metal plate, the flat metal plate is interposed between the two lead wires hermetically insulated and fixed in the flat metal plate through the glass members. Therefore, when the distance between the lead wires is predetermined, the thicknesses of the glass members located between the lead wires are limited. As a result, a capacitance between the lead wires cannot be reduced, and high-speed modulation cannot be easily performed.